It is desirable to have an electrical switch wherein a single arrangement can provide, depending on where the contacts are located, a switch that: (i) is normally open and closes upon activation; (ii) is normally closed and opens upon activation; or (iii) includes a pair of contacts, one being normally open and the other being normally closed, which reverse their respective states upon activation.
Additionally, because of space limitations on a printed wiring board (PWB), it is desirable to provide switching functions in a low profile configuration that mounts onto a PWB. In a telephone set, for example, switches are used to interface between user operated keys, such as a switchhook, and electronic circuitry on the PWB. Such switches frequently include their own special packaging which is not readily adapted to the mechanical configuration of the telephone set.
In U.S. Pat. No. 4,099,037, etitled "Keyboard Switch Assembly Having Cantilevered Leaf Spring Contact Assembly on Common Conductive Frame," pushbutton type keys are shown activating a plurality of normally-open contacts. These contacts are members of a unitary frame, riveted to a substrate over an insulative layer. Although switch packaging is streamlined for telephone set applications, the use of rivets and insulative layers is undesirable. Further, only normally-open (make) contacts are shown, whereas ormally-closed (break) contacts are desirable in many applications. Indeed, mixing make and break contacts in the same keyboard does not appear feasible using the switch structure of the aforementioned patent without introducing another substrate positioned above the unitary frame.
Accordingly, it is an object of the present invention to provide a low cost, low profile electrical switch.
It is another object of the present invention to provide a switch having a plurality of spring members, mounted onto a single substrate, and capable of providing both normally-open and normally-closed contacts.